Each qualified electrician to learn the value of the expected load on the wiring can just choose the cable cross-section of current.The task is simple, face it is taught in every school of a technical profile, from primary to tertiary.It should be remembered that, by choosing the cable, it is preferable to err on the larger than the smaller side.
Industrial enterprises all the necessary calculations are performed by professionals with specialized electrical engineering, so the network settings are not determined on the basis of "paved, that we have", and optimized with regard to minimizing the costs in accordance with technical regulations.There are standard rules of electrical device, that they are guided and engineers, making the choice of cable cross-section of current.RB (Terms device radio installations) are required reading for each designer-electrician.
Difficulties arise when people do not have sufficient qualifications, attempt to make installation or replace the wiring in your home or at the cottage.Selection of the cable cross-section - it is responsible.By doing it wrong, at best, may be faced with having to violate the integrity of the plaster and change the blown lead.About the worst-case scenarios such as fire, I do not even want to mention.
To understand the consequences of mistakes in the selection of the cable should be familiar with fairly simple rules based on a school course of physics.So
:
magnitude of the electrical resistance of a conductor is directly proportional to its length and resistivity.The cross-section on the contrary, affects them in reverse order:
R = (ρ x L) / S,
where:
- R - the resistance, measured in ohms;
- ρ - resistivity, i.e. the resistance of the material of the conductor length of 1 m and a cross section of 1 mm2;
- L - length of the line, m;
- S - cross-sectional area of the conductor mm2.
Resistivity different for different metals.For example, for the silver, it is about 0.016 ohm x mm2 / m2, at a platinum - 0.1, and that of gold - 0.02.However, the choice of cable cross-section of current does not involve the use of precious metals (the reason is clear).
Now load.In order not to err in the amount of current that will flow in the wires, it is enough to know the simple formula of Ohm's law for the circuit with a resistive load:
W = U x I,
where:
- W - power, measured in watts;
- U - voltage (here it is 220 volts);
- I - the amount of current (amps).
In fact, Volt-Amps are different from W, but in terms of premises, which is dominated by the nature of the active load (incandescent lamps, heaters and so on. N.), This difference is negligible.
Putting all electrical power, you can set the size of the load in Watts, which will choose the cable cross-section of current.
Then everything is simple.Since gold or platinum wires is unlikely to use even Abramovich interest other metals more common.If the choice is made in favor of an expensive cable, copper, every square millimeter (or electricians expressed a "square") is able to pass up to 10 amps.In the properties of aluminum modest 8 amps, but it is cheaper.
Usually, the choice of cable cross-section of current in the apartments is made in favor of aluminum wire section and a half square (sockets) and polkvadrata (lighting).Electric cookers and other energy-intensive consumers require separate introductions of the cable conductor cross-section 2.5 mm2.
important to remember that connect the copper wire and aluminum can not be.Such a twist in time loses its conductive properties.
